Sheet feeding device and image forming apparatus incorporating the sheet feeding device

ABSTRACT

A sheet feeding device includes a sheet feeder, a sheet separator, a guide portion, and an adjuster. The sheet feeder is configured to feed a sheet loaded on a sheet loader. The sheet separator is configured to contact the sheet feeder to separate the sheet fed by the sheet feeder. The guide portion is configured to guide the sheet to a contact portion between the sheet feeder and the sheet separator. The adjuster is configured to adjust a position of a downstream end of the guide portion in a sheet conveyance direction.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-222024, filed on Nov. 28, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND Technical Field

This disclosure relates to a sheet feeding device and an image forming apparatus incorporating the sheet feeding device.

Discussion of the Background Art

Various types of sheet feeding devices are known to include a sheet feed body, a sheet separation body, and a guide. The sheet feed body feeds sheets loaded on a sheet loader. The sheet separation body contacts the sheet feed body and separates the sheets fed by the sheet feed body. The guide guides the sheets to a contact portion provided between the sheet feed body and the sheet separation body.

SUMMARY

At least one aspect of this disclosure provides a sheet feeding device including a sheet feeder, a sheet separator, a guide portion, and an adjuster. The sheet feeder is configured to feed a sheet loaded on a sheet loader. The sheet separator is configured to contact the sheet feeder to separate the sheet fed by the sheet feeder. The guide portion is configured to guide the sheet to a contact portion between the sheet feeder and the sheet separator. The adjuster is configured to adjust a position of a downstream end of the guide portion in a sheet conveyance direction.

Further, at least one aspect of this disclosure provides an image forming apparatus including a sheet loader, the above-described sheet feeding device, and an image forming device. The sheet loader is configured to load a sheet. The above-described sheet feeding device is configured to separate the sheet loaded on the sheet loader and feed the sheet. The image forming device is configured to form an image on the sheet fed by the sheet feeding device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

An exemplary embodiment of this disclosure will be described in detail based on the following figured, wherein:

FIG. 1 is an external perspective view illustrating an example of an overall configuration of an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the present embodiment of this disclosure;

FIGS. 3A and 3B are diagrams illustrating a comparative bypass sheet feeder in a sheet feeding operation with a sheet having rigidity such as a thick paper;

FIG. 4 is a diagram illustrating the comparative bypass sheet feeder for explaining a cause of sheet feeding failure explained in FIGS. 3A and 3B;

FIGS. 5A and 5B are diagrams illustrating a guide that reduces an entry angle of a sheet;

FIG. 6 is a perspective view illustrating a bypass tray and a bypass sheet feeder;

FIG. 7 is a perspective view illustrating the bypass sheet feeder;

FIG. 8 is a cross-sectional view illustrating the bypass sheet feeder;

FIG. 9 is a perspective view illustrating a sheet separation unit;

FIG. 10 is a cross-sectional view illustrating a part of the sheet separation unit indicated by a broken line a in FIG. 9;

FIG. 11 is an exploded perspective view illustrating a main part of the sheet separation unit;

FIGS. 12A and 12B are diagrams illustrating the sheet separation unit in adjustment of the position of the tip end of a guide (in other words, the position of the tip end of a nip guide);

FIG. 13 is a diagram illustrating the guide regarding an adjustment range of the guide;

FIG. 14 is a perspective view illustrating the sheet separation unit with a spacer holder to hold a replacement spacer; and

FIG. 15 is a diagram illustrating an example of a document reading device with an automatic document feeder (ADF).

DETAILED DESCRIPTION

It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly.

Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layer and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure.

The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Descriptions are given, with reference to the accompanying drawings, of examples, exemplary embodiments, modification of exemplary embodiments, etc., of an image forming apparatus according to exemplary embodiments of this disclosure. Elements having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted. Elements that do not demand descriptions may be omitted from the drawings as a matter of convenience. Reference numerals of elements extracted from the patent publications are in parentheses so as to be distinguished from those of exemplary embodiments of this disclosure.

This disclosure is applicable to any sheet feeding device and image forming apparatus, and is implemented in the most effective manner in an electrophotographic image forming apparatus.

In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes any and all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of this disclosure are described.

Hereinafter, a detailed description is given of an embodiment of this disclosure with reference to the drawings.

It is to be noted that elements (for example, mechanical parts and components) having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted.

FIG. 1 is an external perspective view illustrating an example of an overall configuration of an image forming apparatus 1 according to an embodiment of this disclosure. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus 1 according to the present embodiment of this disclosure.

The image forming apparatus 1 may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to the present example, the image forming apparatus 1 is an electrophotographic laser printer that forms and prints toner images on recording media by electrophotography.

It is to be noted in the following examples that: the term “image forming apparatus” indicates an apparatus in which an image is formed on a recording medium such as paper, OHP (overhead projector) transparencies, OHP film sheet, thread, fiber, fabric, leather, metal, plastic, glass, wood, and/or ceramic by attracting developer or ink thereto; the term “image formation” indicates an action for providing (i.e., printing) not only an image having meanings such as texts and figures on a recording medium but also an image having no meaning such as patterns on a recording medium; and the term “sheet” is not limited to indicate a paper material but also includes the above-described plastic material (e.g., an OHP sheet), a fabric sheet and so forth, and is used to which the developer or ink is attracted. In addition, the “sheet” is not limited to a flexible sheet but is applicable to a rigid plate-shaped sheet and a relatively thick sheet.

Further, size (dimension), material, shape, and relative positions used to describe each of the components and units are examples, and the scope of this disclosure is not limited thereto unless otherwise specified.

Further, it is to be noted in the following examples that: the term “sheet conveying direction” indicates a direction in which a recording medium travels from an upstream side of a sheet conveying path to a downstream side thereof; the term “width direction” indicates a direction basically perpendicular to the sheet conveying direction.

As illustrated in FIG. 1, the image forming apparatus 1 (for example, a laser printer in this specification) according to the present embodiment of this disclosure includes a sheet tray 30, a sheet ejection tray 19, and a bypass tray 40. The sheet tray 30 loads and contains a sheet bundle including a sheet P. The sheet ejection tray 19 stacks the sheet P that has been ejected from the inside of a housing 10 of the image forming apparatus 1. The bypass tray 40 opens and closes with respect to the housing 10. The sheet tray 30 is provided to be drawable to the front side of the image forming apparatus 1 in FIG. 1.

The image forming apparatus 1 further includes a photoconductor 6, an image forming device 7, a transfer roller 14, and a fixing device 15. The photoconductor 6 functions as a latent image bearer. The image forming device 7 forms a toner image on the surface of the photoconductor 6. The transfer roller 14 transfers the toner image formed on the surface of the photoconductor 6. The fixing device 15 fixes the toner image transferred onto the sheet P, to the sheet P. The image forming device 7 includes a charging unit, an exposure unit, a developing unit, and a cleaning unit. The charging unit uniformly charges the surface of the photoconductor 6. The exposure unit irradiates laser light based on image data, to the surface of the photoconductor 6, so as to form a latent image on the surface of the photoconductor 6. The developing unit develops the latent image formed on the surface of the photoconductor 6, with toner, so as to visualize the latent image to a toner image. The cleaning unit removes residual toner remaining on the surface of the photoconductor 6 after the toner image has been transferred and cleans the surface of the photoconductor 6 for subsequent image formation.

Further, the image forming apparatus 1 includes a sheet feed roller 11 that is disposed below the housing 10. The sheet feed roller 11 that functions as a sheet feeder applies conveying force to the sheet P that has been contained in the sheet tray 30 in which the sheet bundle including the sheet P is contained.

A sheet separation roller 34 is also disposed below the housing 10 of the image forming apparatus 1. The sheet separation roller 34 is disposed to contact the sheet feed roller 11.

Furthermore, the image forming apparatus 1 includes a bypass sheet feed roller 17 and a bypass sheet separation roller 20 on the right side of the housing 10 in FIG. 2. The bypass sheet feed roller 17 that functions as a sheet feeder applies conveying force to the sheet P loaded on the bypass tray 40. The bypass sheet separation roller 20 that functions as a sheet separator contacts the bypass sheet feed roller 17.

When an image is formed by the image forming apparatus 1, the charging unit included in the image forming device 7 uniformly charges the surface of the photoconductor 6, and the exposure unit included in the image forming device 7 forms a latent image on the charged surface of the photoconductor 6. Then, the developing unit included in the image forming device 7 develops the latent image formed on the surface of the photoconductor 6, so that a toner image is formed on the surface of the photoconductor 6.

In a case in which an image is formed on the sheet P that is contained in the sheet tray 30, a sheet feeding device 31 feeds the sheet P loaded on the sheet tray 30.

The sheet feeding device 31 includes a sheet feed roller 11 and a sheet separation roller 34. The sheet feed roller 11 contacts an uppermost sheet of the sheet bundle loaded on the sheet tray 30 and is driven to rotate by a drive source. The sheet separation roller 34 is rotatably supported by a torque limiter and contacts the sheet feed roller 11 by a biasing force of a biasing member to form a sheet separation nip region. The sheet separation roller 34 is rotated together with the sheet feed roller 11.

Sheets P, which are fed from the sheet tray 30 by the sheet feed roller 11 driven and rotated by the drive source, enter the sheet separation nip region between the sheet feed roller 11 and the sheet separation roller 34. In a case in which the sheets P have not entered the sheet separation nip region or in a case in which a single sheet P has entered in the sheet separation nip region, relatively large driving force of the sheet feed roller 11 is applied to the sheet separation roller 34. According to this arrangement, torque of driven rotation of the sheet separation roller 34 exceeds a predetermined threshold value, and therefore the torque limiter allows the driven rotation of the sheet separation roller 34. In other words, in a case in which the sheets P have not entered the sheet separation nip region or in a case in which a single sheet P has entered in the sheet separation nip region, the sheet separation roller 34 is rotated along with the sheet feed roller 11.

On the other hand, in a case in which a plurality of sheets P have entered in layers, the sheet feed roller 11 applies relatively large sheet conveyance force to the uppermost sheet P that directly contacts the sheet feed roller 11 in the sheet separation nip region. Thus, the uppermost sheet P is fed in a sheet conveyance direction. The sheets P other than the uppermost sheet P are pressed in the sheet separation nip region to receive a conveyance resistance. When the conveyance resistance exceeds the frictional resistance between the uppermost sheet P and a second uppermost sheet P, slippage occurs between the sheets, in other words, the uppermost sheet P slips on the second uppermost sheet P. Then, this slippage causes the torque of rotation of the sheet separation roller 34 that is rotated together with the sheet feed roller 11, to be equal to or less than the predetermined threshold value. Therefore, the torque limiter no longer allows the sheet separation roller 34 to rotate together with the sheet feed roller 11. As a result, the conveyance resistance to the second uppermost sheet P and the subsequent sheets P, which are the sheets after the second uppermost sheet P, further increases to stop movement of the second uppermost sheet P and the subsequent sheets P. Thus, the sheet separation roller 34 separates the uppermost sheet P from the other sheets P while applying the conveyance resistance to the plurality of sheets P.

A single sheet, a sheet P, is separated from the other sheets P in the sheet separation nip region, and reaches a sheet conveyance passage 18. Then, the sheet P is conveyed by a pair of sheet conveying rollers 12 including two sheet conveying rollers 12 a and 12 b, to a position at which the sheet P1 contacts a pair of registration rollers 13.

In a case in which an image is formed on the sheets P loaded on the bypass tray 40, a bypass sheet feeding device 41 that functions as a sheet feeding device feeds the sheets P loaded on the bypass tray 40.

The bypass sheet feeding device 41 has a configuration similar to the configuration of the sheet feeding device 31. As described above, the bypass sheet feeding device 41 includes a bypass sheet feed roller 17 and a bypass sheet separation roller 20. The bypass sheet feed roller 17 contacts an uppermost sheet P of a sheet bundle loaded on the bypass tray 40 and is driven to rotate by the drive source. The bypass sheet separation roller 20 is rotatably supported by the torque limiter and contacts the bypass sheet feed roller 17 by the biasing force of the biasing member to form a bypass separation nip region N (see FIG. 13). The bypass separation nip region N functions as a contact portion of the bypass sheet feed roller 17 and the bypass sheet separation roller 20. The bypass sheet separation roller 20 is rotated together with the bypass sheet feed roller 17.

The sheet P, which is fed from the bypass tray 40 by the bypass sheet feed roller 17 that is driven and rotated by the drive source, enters the bypass separation nip region N between the bypass sheet feed roller 17 and the bypass sheet separation roller 20. Similar to the sheet feeding device 31, when a plurality of sheets has been conveyed to the bypass separation nip region N, rotations of the bypass sheet separation roller 20 together with rotations of the bypass sheet feed roller 17 is restricted by the torque limiter, and the uppermost sheet P is separated from the other sheets P.

Then, the pair of registration rollers 13 is driven and rotated in synchronization with the timing at which the toner image formed on the surface of the photoconductor 6 reaches a transfer position opposed to the transfer roller 14, and the toner image formed on the surface of the photoconductor 6 is transferred onto the surface of the sheet P at the transfer position. After the toner image has been transferred onto the sheet P, the toner image formed on the sheet P is fixed by application of heat and pressure in the fixing device 15. Then, a pair of sheet ejection rollers 16 ejects the fixed sheet P to the sheet ejection tray 19 outside the image forming apparatus 1.

A comparative sheet feeding device discloses that an angle (i.e., an incidence angle) is set to 50 degrees or smaller, between an extended line of a nip region that is a contact portion where a sheet feed roller that functions as a sheet feed body and a sheet separation roller that functions as a sheet separation body contact, and a tangent line of the sheet feed roller at the contact position of a sheet loaded on a sheet loader and the sheet feed roller.

However, the position of the guide at the downstream end of the guide in the sheet feeding direction varies due to a manufacturing error, for example, and it is likely to cause multi feeding and sheet feeding failure when feeding a sheet having rigidity.

FIGS. 3A and 3B are diagrams illustrating a comparative bypass sheet feeder in a sheet feeding operation with a sheet Pa having rigidity such as a thick paper.

As illustrated in FIG. 3A, a bypass sheet separation roller 520 is rotatably supported in a direction to contact to and separate from a bypass sheet feed roller 517 at a fulcrum X. In addition, the bypass sheet separation roller 520 is biased by a spring 526 that functions as a biasing body, toward the bypass sheet feed roller 517. The leading end of the sheet P that is fed by the bypass sheet feed roller 517 contacts the bypass sheet separation roller 520, and receives sheet conveyance force from the bypass sheet separation roller 20 to be conveyed toward a bypass separation nip region.

As the leading end of the sheet Pa contacts the bypass sheet separation roller 520, the bypass sheet separation roller 520 is pressed in a direction to separate from the bypass sheet feed roller 517. In a case in which a sheet having small rigidity such as a plain paper is pressed in the direction to separate from the bypass sheet feed roller 517, the leading end of the sheet having small rigidity is warped due to reaction force of the bypass sheet separation roller 520 generated when the bypass sheet separation roller 520 is pressed in the direction to separate from the bypass sheet feed roller 517. According to this configuration, the leading end of the sheet is conveyed to the bypass separation nip region by rotating the bypass sheet separation roller 520 together with the bypass sheet feed roller 517, without causing the bypass sheet separation roller 520 to separate from the bypass sheet feed roller 517.

However, in a case in which a sheet having large rigidity such as a thick paper is pressed in the direction to separate from the bypass sheet feed roller 517, the leading end of the sheet having large rigidity is not warped due to reaction force of the bypass sheet separation roller 520, and therefore the bypass sheet separation roller 520 is pressed in the direction to separate from the bypass sheet feed roller 517. Consequently, as illustrated in FIG. 3B, the bypass sheet separation roller 520 is rotated in the direction to separate from the bypass sheet feed roller 517 against the biasing force of the spring 526, thereby separating from the bypass sheet feed roller 517. Thus, when the bypass sheet separation roller 520 is separated from the bypass sheet feed roller 517, the bypass sheet separation roller 520 is stopped rotating, and therefore the sheet conveyance force of the bypass sheet separation roller 520 is not applied to the leading end of the sheet in contact with the bypass sheet separation roller 520. As a result, the sheet is not conveyed, causing sheet feeding failure.

FIG. 4 is a diagram illustrating the comparative bypass sheet feeder for explaining a cause of poor sheet feeding in FIGS. 3A and 3B.

As illustrated by the broken line illustrated in FIG. 4, if an angle of entry θ1 of the sheet Pa to the bypass sheet separation roller 520 is large (in other words, if an angle of the sheet Pa and a tangent line direction of the bypass sheet separation roller 520 is large at a contact position T where the leading end of the sheet P contacts the bypass sheet separation roller 520), when the leading end of the sheet P contacts the bypass sheet separation roller 520, force to be applied to the bypass sheet separation roller 520 (that is, sheet conveyance force of the bypass sheet feed roller 517) has small component force to cause the leading end of the sheet P is conveyed in a tangent line direction toward the bypass sheet separation roller 520, and large component force to cause the bypass sheet separation roller 520 to separate from the bypass sheet feed roller 517 in a direction perpendicular to the tangent line direction.

In a case in which the sheet having small rigidity is fed, when the leading end of the sheet P comes into contact with the bypass sheet separation roller 520, the leading end of the sheet Pa is warped (curved), and therefore the component force in the tangent line direction becomes large and the component force in the direction perpendicular to the tangent line direction becomes small. According to this configuration, the bypass sheet separation roller 520 is rotated with the bypass sheet feed roller 517 without separating from the bypass sheet feed roller 517, and therefore the bypass sheet separation roller 520 conveys the leading end of the sheet to the bypass separation nip region.

However, in a case in which the sheet having large rigidity is fed, when the leading edge of the sheet Pa comes into contact with the bypass sheet separation roller 520, the leading edge of the sheet Pa is not warped (curved). Therefore, while maintaining the large component force to separate the bypass sheet separation roller 520 from the bypass sheet feed roller 517 in the direction perpendicular to the tangent line direction, the sheet Pa is continuously pressed in the direction to separate the bypass sheet separation roller 520 from the bypass sheet feed roller 517. As a result, the bypass sheet separation roller 520 is separated from the bypass sheet feed roller 517, causing sheet feeding failure.

By contrast, as indicated by a solid line in FIG. 4, if an angle of entry θ2 of the sheet P to the bypass sheet separation roller 520 is small (in other words, if an angle of the sheet Pa and the tangent line direction of the bypass sheet separation roller 520 is small at the contact position T), when the leading end of the sheet Pa contacts the bypass sheet separation roller 520, force to be applied to the bypass sheet separation roller 520 has large component force to cause the leading end of the sheet Pa is conveyed in the tangent line direction toward the bypass sheet separation roller 520, and small component force to cause the bypass sheet separation roller 520 to separate from the bypass sheet feed roller 517 in the direction perpendicular to the tangent line direction. Thus, since the component force in the direction perpendicular to the tangent line direction is small, even if the sheet Pa with high rigidity contacts the bypass sheet separation roller 520, the bypass sheet separation roller 520 is not separated from the bypass sheet feed roller 517, and therefore the leading end of the sheet Pa is conveyed to the bypass separation nip region. Accordingly, by reducing the angle of entry of the sheet Pa to the bypass sheet separation roller 520, even a sheet with high rigidity is fed and conveyed preferably.

When considering a reduction in the angle of entry of the sheet Pa to the bypass sheet separation roller 520, for example, it is effective to reduce an angle of inclination of the bypass tray 40. However, if the angle of inclination of the bypass tray 40 is reduced, the size of an image forming apparatus (i.e., the image forming apparatus 1) increases when the bypass tray 40 is opened. Consequently, a sufficient space around the image forming apparatus 1 may need to be additionally provided to open the bypass tray 40 reliably.

In the present embodiment, in order to address this inconvenience, a guide is disposed upstream from the bypass separation nip region N in the sheet conveyance direction. The guide is made of a resin sheet having a coefficient of friction to the sheet smaller than a coefficient of friction of the bypass sheet separation roller 20 to the sheet. The guide is configured to guide the leading end of the sheet to the sheet separation nip region. It is to be noted that the “sheet conveyance direction” indicates a direction of conveyance of a sheet in the bypass separation nip region N.

FIGS. 5A and 5B are diagrams illustrating a guide 22 that reduces an angle of entry 0 of a sheet P to the bypass sheet separation roller 20.

As illustrated in FIGS. 5A and 5B, by disposing the guide 22 upstream from the bypass separation nip region N in the sheet conveyance direction, the leading end of the sheet fed from the bypass tray 40 contacts the guide 22 that is made of a resin sheet. Since the coefficient of friction of the guide 22 to the sheet is smaller than the coefficient of friction of the bypass sheet separation roller 20 to the sheet, even if the angle of entry of the leading end of the sheet P to the guide 22 (i.e., an angle of the surface of the guide 22 and the sheet P) is large, the leading end of the sheet P slides on the surface of the guide 22. Therefore, the sheet P is guided to the bypass separation nip region N while the leading end of the sheet P is warped (curved). After having passed the guide 22, the leading end of the sheet P contacts the surface of the bypass sheet separation roller 20 to be conveyed to the bypass separation nip region N.

The guide 22 has a nip guide portion 22 a to guide the leading end of the sheet P to the bypass separation nip region N. As can be seen from FIGS. 5A and 5B, as the leading end of the nip guide portion 22 a of the guide 22 moves away from the bypass separation nip region N, a position at which the leading end of the sheet P contacts the surface of the bypass sheet separation roller 20 is brought to be further away from the bypass separation nip region N. As a result, the angle of entry θ increases. Therefore, it is preferable to dispose the guide 22 so that the tip of the nip guide portion 22 a that functions as a guide portion of the guide 22, to guide the sheet P to the bypass separation nip region N is brought to be closer to the bypass separation nip region N.

As described above, by disposing the leading end of the sheet P to be located at a position closer to the bypass separation nip region N, with the guide 22, even if the angle of inclination of the bypass tray 40 is relatively large, the angle of entry θ of the leading end of the sheet P to the bypass sheet separation roller 20 is reduced. This configuration prevents an increase in size of the image forming apparatus 1 when the bypass tray 40 is opened. Therefore, sheet feeding failure is restrained.

However, the position of the tip of the nip guide portion 22 a of the guide 22 may vary due to manufacturing errors of the image forming apparatus, and the position of the tip of the nip guide portion 22 a may be away from the bypass separation nip region N farther than the target position. As a result, the angle of entry θ of the leading end of the sheet P to the bypass sheet separation roller 20 increases, and therefore it is likely that sheet feeding failure occurs when feeding a sheet having high rigidity.

Further, it is likely that the tip of the nip guide portion 22 a of the guide 22 enters the bypass separation nip region N due to manufacturing errors of the image forming apparatus. Thus, in a case in which the tip of the nip guide portion 22 a enters the bypass separation nip region N, when a plurality of sheets P enters the bypass separation nip region N, the friction force generating between the sheets P and the nip guide portion 22 a is applied as conveyance resistance, to the second and subsequent sheets. As described above, since the guide 22 has a lower coefficient of friction with respect to the sheet P than the bypass sheet separation roller 20, the conveyance resistance due to the frictional force of the sheet and the nip guide portion 22 a is less than the static frictional force between the uppermost sheet and the second (subsequent) sheet. As a result, no slippage occurs between the uppermost sheet and the second sheet. Therefore, the sheets are not separated in the bypass separation nip region N, and may result in occurrence of multiple sheet feeding.

In order to address this inconvenience, the position of the tip of the nip guide portion 22 a of the guide 22 is adjustable in this embodiment.

Next, a description is given of the detailed configurations of the bypass tray 40 and the bypass sheet feeding device 41, with reference to FIGS. 6 to 9.

FIG. 6 is a perspective view illustrating the bypass tray 40 and the bypass sheet feeding device 41. FIG. 7 is a perspective view of the bypass sheet feeding device 41. FIG. 8 is a cross-sectional view illustrating the bypass sheet feeding device 41. FIG. 9 is a perspective view illustrating a sheet separation unit 42.

As illustrated in FIG. 6, the bypass tray 40 includes a bypass bottom plate 40 a that functions as a sheet loader. The bypass bottom plate 40 a is rotatably supported with an upstream side end portion in the sheet conveyance direction as a fulcrum. The upstream side end portion in the sheet conveyance direction of the bypass bottom plate 40 a is supported by a support shaft 40 b and is rotatably (swingably) supported by the bypass tray 40 with the support shaft 40 b as a fulcrum.

In a standby state, the bypass bottom plate 40 a is located at a position indicated by a broken line in FIG. 8. When feeding a sheet, the upstream side end portion in the sheet conveyance direction of the bypass bottom plate 40 a is lifted along with rotation of the support shaft 40 b, so that the uppermost sheet P of the sheet bundle loaded on the bypass bottom plate 40 a is brought to contact the bypass sheet feed roller 17.

The bypass bottom plate 40 a is provided with side fences 43 in pair. The side fences 43 regulate the position at both ends in a width direction perpendicular to the sheet conveyance direction of the sheet P loaded on the bypass bottom plate 40 a. The side fences 43 are slidable in the width direction by moving simultaneously with each other.

A friction plate 40 c is disposed at a center of the bypass bottom plate 40 a in the width direction of a downstream end in the sheet conveyance direction.

As illustrated in FIGS. 6 and 7, the bypass sheet feed roller 17 that functions as a sheet feeding body is mounted on the tip of a rotary shaft 17 a extending from one end of the image forming apparatus 1 to the center in the width direction of the image forming apparatus 1. A driving force is transmitted from a drive source to the rotary shaft 17 a of the bypass sheet feed roller 17 to rotate the rotary shaft 17 a of the bypass sheet feed roller 17. The bypass sheet feed roller 17 is mounted on the rotary shaft 17 a so as to rotate together with the rotary shaft 17 a.

The bypass sheet separation roller 20 that functions as a sheet separation body is provided in the sheet separation unit 42. The sheet separation unit 42 is fixed by screws 24 a to a sheet conveyance guide 25 that guides the sheet P after the sheet P has passed through the bypass separation nip region N.

The sheet separation unit 42 includes a base 21 that supports the bypass sheet separation roller 20 to contact and separate with respect to the bypass sheet feed roller 17 and to be rotatable together with the bypass sheet feed roller 17. As illustrated in FIG. 8, a spring 26 is mounted on the base 21 to bias the bypass sheet separation roller 20 toward the bypass sheet feed roller 17.

The guide 22 that is made of a resin sheet is fixed to a guide holding member 23 that is made of a sheet metal, with an adhesive, a double-sided tape, or the like.

The guide holding member 23 that functions as a guide holder has a guide positioning projection 23 a. The upstream side end portion in the sheet conveyance direction of the guide 22 is brought to contact (abut against) the guide positioning projection 23 a. Consequently, the guide 22 is held by and fixed to the guide holding member 23, thereby restraining the guide 22 from being fixed to the guide holding member 23 obliquely to the sheet conveyance direction. The guide holding member 23 is screwed to the base 21 with a screw 27 through a spacer 29 that functions as an adjuster.

The guide 22 is longer than the bypass sheet separation roller 20 in the length in the width direction of the sheet P. The width direction of the sheet P is a direction perpendicular to the sheet conveyance direction of the sheet P. The guide 22 further has a nip guide portion 22 a and outer guide portions 22 b (see FIG. 9). The nip guide portion 22 a contacts the surface of the bypass sheet separation roller 20 and guides a sheet to the bypass separation nip region N. The outer guide portions 22 b are provided on both sides in the width direction of the nip guide portion 22 a and extend further downstream from the bypass separation nip region N in the sheet conveyance direction (see FIG. 9). As described above, the guide 22 is made longer than the bypass sheet separation roller 20 in the length in the width direction of the sheet conveyance direction and the outer guide portions 22 b are extended further downstream from the bypass separation nip region N in the sheet conveyance direction, so that the sheet P is guided stably.

Further, the base 21 has a mounting portion 21 c that extends in a vertical direction. Screw through holes 122 c are formed on both sides in the width direction of the mounting portion 21 c. The screws 24 a go through the respective screw through holes 122 c. By placing the mounting portion 21 c of the base 21 on a base 25 a of the sheet conveyance guide 25 and inserting the screws 24 a that have been placed in the respective screw through holes 122 c into respective screw holes in the base 25 a, the sheet separation unit 42 is screwed to the sheet conveyance guide 25.

Further, the base 21 is provided with a leading end regulating portion 21 a that regulates the position of the sheet P in the sheet conveyance direction, by causing the leading end of the sheet P loaded on the bypass bottom plate 40 a to contact the base 21 in the standby state (See FIG. 8).

FIG. 10 is a cross-sectional view illustrating a part of the sheet separation unit 42 indicated by a broken line a in FIG. 9.

As illustrated in FIG. 10, in the present embodiment, the fixing surface of the guide 22 to the guide holding member 23 is provided by β mm below a top C of the bypass sheet separation roller 20, and the tip of the nip guide portion 22 a continuously contacts the bypass sheet separation roller 20. As described above, by causing the tip of the nip guide portion 22 a to contact the bypass sheet separation roller 20, no variation occurs in positional relation in the vertical direction of the nip guide portion 22 a and the bypass sheet separation roller 20 due to parts variation. Accordingly, by adjusting the position of the tip of the nip guide portion 22 a in the sheet conveyance direction, the angle of entry of the sheet P is set to be a target angle of entry with accuracy.

In the present embodiment, the guide 22 is a resin sheet and is fixed to the guide holding member 23 in a cantilevered manner, so that the nip guide portion 22 a that is the leading end side of the guide 22 is elastically deformable. Accordingly, the nip guide portion 22 a follows the surface of the bypass sheet separation roller 20, and therefore the contact state of the nip guide portion 22 a and the bypass sheet separation roller 20 is maintained.

It is to be noted that, in the present embodiment, the tip of the nip guide portion 22 a is constantly in contact with the bypass sheet separation roller 20. However, the configuration is not limited to the above-described configuration. For example, the tip of the nip guide portion 22 a may not be in contact with the bypass sheet separation roller 20.

FIG. 11 is an exploded perspective view illustrating the main part of the sheet separation unit 42.

As illustrated in FIG. 11, the sheet separation unit 42 includes a guide mounting face 21 f of the base 21. The guide mounting face 21 f extends in a direction perpendicular to the sheet conveyance direction in which the guide holding member 23 is attached. On the guide mounting face 21 f, a screw hole 21 g and a positioning projection 21 b are aligned in the width direction. Screw groove is formed on the inner circumferential surface of the screw hole 21 g. Further, a spacer mounting guide 21 e that extends toward the upstream side in the sheet conveyance direction is provided to the guide mounting face 21 f.

The guide holding member 23 has a symmetrical shape with respect to the center portion in the width direction. Fixing portions 23 b are provided on both sides in the width direction. A screw through hole 23 c and a positioning hole 23 d are formed in each of the fixing portions 23 b. The screw 27 passes through the screw through hole 23 c and the positioning projection 21 b passes through the positioning hole 23 d. The positioning hole 23 d is provided to one end side in the width direction of the fixing portions 23 b, as illustrated in FIG. 11. The positioning hole 23 d has a slot shape extending in the width direction and is a secondary reference (i.e., a sub reference) for positioning. On the other hand, the positioning hole 23 d provided on the other end side of the fixing portions 23 b in the width direction is a round hole that has an inner diameter substantially the same as the outer diameter of the positioning projection 21 b. The positioning hole 23 d on the other end side of the fixing portions 23 b is a main reference for positioning.

The spacer 29 that functions as an adjuster is a planar member made of metal, resin, or the like. The spacer 29 has an outer shape that is the same as the shape of the guide mounting face 21 f of the base 21, and has a cut portion 29 c on the outer side of the lower end in the width direction. Further, the spacer 29 is provided with a projection through hole 29 a and a screw through hole 29 b aligned in the width direction. The positioning projection 21 b passes through the projection through hole 29 a. The screw 27 passes through the screw through hole 29 b.

If the spacer 29 is to be mounted on the guide mounting face 21 f with the spacer 29 being upside down, the position of the projection through hole 29 a of the spacer 29 in the vertical direction with respect to the positioning projection 21 b of the base 21 and the position of the screw through hole 29 b of the spacer 29 in the vertical direction with respect to the screw hole 21 g of the base 21 are different (deviated). Therefore, the spacer 29 is not mounted on the guide mounting face 21 f. Similarly, even if the spacer 29 is to be mounted on the guide mounting face 21 f with the spacer 29 being flipped horizontally (left and right) or being mirror-reversed, the position of the projection through hole 29 a of the spacer 29 in the width direction with respect to the positioning projection 21 b of the base 21 and the position of the screw through hole 29 b of the spacer 29 in the width direction with respect to the screw hole 21 g of the base 21 are shifted (deviated). Therefore, the spacer 29 is not mounted on the guide mounting face 21 f.

If the spacer 29 has a simple rectangular shape, it is difficult to determine visually whether the spacer 29 is disposed upside down or flipped horizontally with respect to the correct position, thereby resulting in the poor mounting operability. However, as in the present embodiment, by providing the cut portion 29 c in the spacer 29, it is easy to determine visually whether the spacer 29 is at the correct position, thereby enhancing the mounting operability of the spacer 29.

Further, by providing the spacer mounting guide 21 e on the guide mounting face 21 f, in a case in which the spacer 29 is to e mounted while being upside down or is flipped horizontally with respect to the correct position, the spacer 29 contacts the spacer mounting guide 21 e. Therefore, a user easily recognizes that the spacer 29 is not mounted with the correct position. Consequently, the mounting operability is enhanced.

Further, by making the outer shape of the spacer 29 identical to the outer shape of the guide mounting face 21 f, a bottom face 29 e of the spacer 29 is brought to contact the mounting portion 21 c of the base 21 and an inner side face 29 d of the spacer 29 is brought to contact a side wall face 21 h of a containing portion 21 i of the base 21 in which the bypass sheet separation roller 20 is stored, so that the spacer 29 is caused to slide toward the guide mounting face 21 f. By simply sliding the spacer 29, the positioning projection 21 b passes through the projection through hole 29 a, thereby mounting the spacer 29 on the guide mounting face 21 f. Thus, with a single operation of sliding the spacer 29, the spacer 29 is mounted on the guide mounting face 21 f, and therefore the mounting operability of the spacer 29 is enhanced.

Further, in the present embodiment, the spacer 29 is provided with the projection through hole 29 a and the screw through hole 29 b. With this configuration, the positioning projection 21 b and the screw 27 pass through the spacer 29. Consequently, the spacer 29 is prevented from rotating about the positioning projection 21 b or the screw 27 and part of the spacer 29 is prevented from projecting from a top end of the guide mounting face 21 f.

Furthermore, in the present embodiment, the bottom face 29 e of the spacer 29 contacts the mounting portion 21 c of the base 21 to be mounted on the guide mounting face 21 f while the inner side face 29 d of the spacer 29 is in contact with the side wall face 21 h of the containing portion 21 i. Since this configuration is also provided in the present embodiment, even if either one of the positioning projection 21 b and the screw 27 is provided, the spacer 29 is prevented from rotating about the one of the positioning projection 21 b and the screw 27, and the part of the spacer 29 is prevented from projecting from the top end of the guide mounting face 21 f.

As described above, once the spacer 29 is mounted on the guide mounting face 21 f, the positioning projection 21 b is inserted into the positioning hole 23 d of the guide holding member 23 to position the guide holding member 23 to the base 21 via the spacer 29. In other words, the guide holding member 23 is attached to the base 21 and the spacer 29 is disposed between the guide holding member 23 and the base 21. Then, the guide holding member 23 is screwed to the base 21 with the screw 27. As a result, the spacer 29 is held and fixed between the guide mounting face 21 f of the base 21 and the fixing portions 23 b of the guide holding member 23.

Next, a description is given of adjustment of the position of the tip of the guide 22 (that is, the position of the tip of the nip guide portion 22 a).

FIGS. 12A and 12B are diagrams illustrating the sheet separation unit 42 in adjustment of the position of the tip of the guide 22 (i.e., the position of the tip of the nip guide portion 22 a).

FIG. 12A illustrates a state in which the spacer 29 that is a reference spacer is mounted on the base 21, and FIG. 12B illustrates a state in which a spacer having a thickness thinner than the reference spacer (i.e., the spacer 29) is mounted on the base 21. Hereinafter, the spacer 29 is occasionally referred to as the reference spacer 29.

In the present embodiment, as illustrated in FIG. 12A, the sheet separation unit 42 is designed such that the tip of the nip guide portion 22 a of the guide 22 comes to a target position with the reference spacer (i.e., the spacer 29) mounted on the base 21. In a case in which the tip of the nip guide portion 22 a of the guide 22 is located upstream from the target position in the sheet conveyance direction due to a manufacturing error or errors, the reference spacer 29 is removed and a thin spacer 129 that has a thickness thinner than the reference spacer 29 is mounted on the base 21. The thin spacer 129 functions as an adjuster. According to this configuration, the position of the tip of the nip guide portion 22 a is shifted to a downstream side in the sheet conveyance direction when compared with the configuration with the reference spacer 29 mounted. Accordingly, the position of the tip of the nip guide portion 22 a is brought to the target position that is closer to the bypass separation nip region N.

In a case in which the tip of the nip guide portion 22 a enters the bypass separation nip region N with the reference spacer 29 mounted, the reference spacer 29 is replaced with a thick spacer having a thickness thicker than the reference spacer 29. As a result, the position of the tip of the nip guide portion 22 a shifts to the upstream side in the sheet conveyance direction when compared with the position of the tip of the nip guide portion 22 a with the reference spacer 29 mounted. Accordingly, the tip of the nip guide portion 22 a is brought to a position where the nip guide portion 22 a has not entered.

Thus, in the present embodiment, by mounting a spacer as an adjuster having a different thickness from a reference spacer, the position of the tip of the nip guide portion 22 a is adjusted, and therefore the tip of the nip guide portion 22 a is set to the target position near the bypass separation nip region N.

The thickness of a spacer can be prepared in units of 0.1 mm. Therefore, very fine adjustment can be performed by combining spacers having different thicknesses, and the position of the tip of the nip guide portion 22 a is adjusted with high accuracy.

Further, in the present embodiment, the adjustment is performed simply by removing the guide holding member 23 from the base 21 and replacing the spacer. Accordingly, a user adjusts the position of the tip of the nip guide portion 22 a. For example, in a case in which sheet feeding failure occurs frequently when feeding a rigid sheet, the user replaces the currently mounted spacer with a thinner spacer to adjust the position of the tip (the end) of the nip guide portion 22 a to be located to the further downstream side in the sheet conveyance direction. Further, in a case in which multiple sheet feeding occurs frequently, the user replaces the currently mounted spacer with a thicker spacer to adjust the position of the tip of the nip guide portion 22 a to be located to the further upstream side in the sheet conveyance direction.

FIG. 13 is a diagram illustrating the guide 22 regarding an adjustment range of the guide 22.

The tip of the nip guide portion 22 a (in other words, the downstream end of the nip guide portion 22 a in the sheet conveyance direction) illustrated in FIG. 13 does not affect the separation performance in the bypass separation nip region N, before the tip of the nip guide portion 22 a comes to a position X2 which is the extreme upstream end in the sheet conveyance direction where the tip of the nip guide portion 22 a contacts both the bypass sheet separation roller 20 and the bypass sheet feed roller 17. In a case in which the tip of the nip guide portion 22 a is located downstream from the position X2 in the sheet conveyance direction, the contact pressure in the bypass separation nip region N decreases due to the thickness of the guide 22, which is likely to adversely affect the separation performance. Accordingly, the position of the tip of the nip guide portion 22 a is adjusted to be located upstream from the position X2, as a start point, in the sheet conveyance direction.

Further, when an upstream side end portion of the guide 22 (the guide holding member 23) in the sheet conveyance direction, which is referred to as an upstream side end portion γ1, comes in a swing range (in other words, a rotatable range) of the bypass bottom plate 40 a, which is indicated with a wave line ε in FIG. 13, the bypass bottom plate 40 a contacts (abuts against) the guide holding member 23, and therefore the bypass bottom plate 40 a is prevented from swinging (rotating). In other words, the upstream side end portion γ1 of the guide 22 in the sheet conveyance direction is located downstream from the swing range ε of the bypass bottom plate 40 a in the sheet conveyance direction. For this reason, the position of the tip of the nip guide portion 22 a is adjusted to prevent the guide holding member 23 from entering the swing range of the bypass bottom plate 40 a.

For example, when the tip of the nip guide portion 22 a is located at a target position X1 due to a manufacturing error or errors, the upstream side end portion γ1 of the guide holding member 23 may enter the swing range of the bypass bottom plate 40 a. The swing range is indicated as the wave line ε in FIG. 13. In this case, the tip of the nip guide portion 22 a is adjusted so as to be positioned between the target position X1 and the position X2 in FIG. 13, and to prevent the upstream side end portion γ1 of the guide holding member 23 from entering the swing range of the bypass bottom plate 40 a.

When adjusting the position of the tip of the nip guide portion 22 a in the factor, images near the bypass separation nip region N are taken by camera. If the images indicate that the tip of the nip guide portion 22 a is located between the target position X1 and the position X2 and the upstream side end portion γ1 of the guide holding member 23 is not within the swing range of the bypass bottom plate 40 a indicated by as the wave line ε in FIG. 13, it is determined that no adjustment needs to be performed, and therefore the reference spacer 29 is not replaced with another spacer.

By contrast, if the images indicate that the tip of the nip guide portion 22 a is located downstream from the position X2 in the sheet conveyance direction in FIG. 13, a distance from the position X2 to the tip of the nip guide portion 22 a and a distance from the upstream side end portion γ1 in the sheet conveyance direction to the swing range of the bypass bottom plate 40 a are checked. Then, the thickness of a spacer to be replaced is obtained based on the distance from the position X2 in FIG. 13 to the tip of the nip guide portion 22 a and the distance from the upstream side end portion γ1 in the sheet conveyance direction to the swing range of the bypass bottom plate 40 a, and an appropriate spacer is selected and replaced.

When the upstream side end portion γ1 in the sheet conveyance direction of the guide holding member 23 is within the swing range of the bypass bottom plate 40 a, the thickness of a spacer to be replaced is obtained based on the distance from the tip of the nip guide portion 22 a to the position X2 and a distance required for the upstream side end portion γ1 of the guide holding member 23 in the sheet conveyance direction to move out from the swing range, and an appropriate spacer is selected and replaced.

Further, FIG. 14 is a perspective view illustrating the sheet separation unit with a leaf spring 28 that functions as a spacer holder to hold a replacement spacer. As illustrated in FIG. 14, the spacer 29 may be held by the base 21. In the configuration illustrated in FIG. 14, the leaf spring 28 is mounted on the mounting portion 21 c of the base 21 to hold the replacement spacer, which is the thin spacer 129. The thin spacer 129 (the replacement spacer) is held by being interposed between the leaf spring 28 and the mounting portion 21 c of the base 21. Hereinafter, the thin spacer 129 is occasionally referred to as a replacement thin spacer 129.

For example, in a case in which sheet feeding failure frequently occurs when feeding a rigid sheet, the reference spacer 29 that is currently mounted is replaced with the replacement thin spacer 129 having a thickness thinner than the reference spacer 29, so as to adjust the position of the tip of the nip guide portion 22 a to the downstream side in the sheet conveyance direction.

Further, in a case in which multiple sheet feeding occurs frequently, the reference spacer 29 that is currently mounted is mounted together with the replacement thin spacer 129 in layers, so that the position of the tip of the nip guide portion 22 a is adjusted to the upstream side in the sheet conveyance direction.

As illustrated in FIG. 14, by holding the replacement thin spacer 129 in the sheet separation unit 42, the position of the tip of the nip guide portion 22 a is adjusted on the spot without wasting time to search a replacement spacer (e.g., the replacement thin spacer 129).

It is to be noted that the above-described configuration is applied to the bypass sheet feeding device 41, but this disclosure is also applicable to the sheet feeding device 31. Further, this disclosure is also applicable to an original document feeding device for feeding an original document set on a document sheet tray of an automatic document feeder (ADF).

FIG. 15 is a diagram illustrating an example of a document reading device 100, provided with an automatic document feeder 200.

Hereinafter, the automatic document feeder 200 is occasionally referred to as the ADF 200.

The document reading device 100 includes the ADF 200 and a housing 300. The ADF 200 conveys an original document placed on the original document table 102 to a document reading position (indicated by a triangle mark in FIG. 15) in a given sheet conveyance direction (indicated by arrow in FIG. 15), and align and eject the scanned original document in a document ejection tray 114. The ADF 200 is disposed (mounted) on the housing 300. It is to be noted that the ADF 200 is configured to be openable and closable with respect to the housing 300 by a connecting member such as a hinge. In addition, the bottom surface of the ADF 200 functions as a pressure plate that presses down the original document placed on an exposure glass 302 b when the ADF 200 is closed.

The housing 300 includes a reading portion 301 in which the original document that is conveyed to the document reading position on either a slit exposure glass 302 a or the exposure glass 302 b. The reading portion 301 is movable in a left and right directions (in other words, a horizontal direction).

The ADF 200 includes the original document table 102, a document feeding device 109, various pairs of document conveying rollers (which are a pair of contact rollers 107, a pair of entrance rollers 108, a pair of exit rollers 110, and a pair of document ejection rollers 111), various sensors (for example, optical reflection type sensors) (which are a contact sensor 112, a registration sensor 113, and a document ejection sensor 115), and the document ejection tray 114. The document feeding device 109 includes a document feed roller 103 and a document separation roller 105 that contacts the document feed roller 103 to form a document separation nip region. The original document table 102, the document feeding device 109, the pairs of document conveying rollers (which are the pair of contact rollers 107, the pair of entrance rollers 108, the pair of exit rollers 110, and the pair of document ejection rollers 111), the sensors (which are the contact sensor 112, the registration sensor 113, and the document ejection sensor 115), and the document ejection tray 114 are disposed along a document conveyance passage.

Here, the original document table 102 includes a rotatable bottom plate 102 a and a fixed bottom plate 102 b. The fixed bottom plate 102 b loads a bundle of original documents and is fixed to the original document table 102. The rotatable bottom plate 102 a is supported to rotate about an upstream side end in the sheet conveyance direction. As the rotatable bottom plate 102 a rotates, the leading end of the bundle of original documents set on the original document table 102 is lifted, so that an uppermost original document placed on top of the bundle of original documents is brought to contact the document feed roller 103.

The document feeding device 109 has the configuration substantially identical to the bypass sheet feeding device 41 and the sheet feeding device 31 described above. Specifically, the document feeding device 109 separates and feeds the original documents one by one from the bundle of original documents (or multiple original documents) loaded on the original document table 102.

The contact sensor 112, the pair of contact rollers 107, and the registration sensor 113 compose a registration portion. The registration portion primarily contacts and aligns the original document fed from the document feeding device 109, and pulls out and conveys the original document that has been aligned. The pair of entrance rollers 108 and the pair of exit rollers 110 compose a reverse conveyance portion. The reverse conveyance portion reverses the original document conveyed from the registration portion, and conveys the original document to the exposure glass 30 a so that a document face of the original document to be scanned from below the slit exposure glass 302 a.

A conveyance gap near a reading position of the reverse conveyance portion is set to be as narrow as possible, so that a degree of freedom of the original document is extremely restrained. For example, the conveyance gap between the slit exposure glass 302 a and a white background panel 104 that is disposed facing the slit exposure glass 302 a is extremely narrowed to restrain deterioration of the reading accuracy.

The document ejection sensor 115 and the pair of document ejection rollers 111 compose a document ejection portion. After the original document is scanned, the document ejection portion conveys the original document to the document ejection tray 114. The document ejection tray 114 composes a document stacking portion to load and store the scanned original document.

This disclosure is applied to the document feeding device 109 of the ADF 200 illustrated in FIG. 15.

Further, it is to be noted that the image forming apparatus 1 that employs electrophotography is applied in the present embodiment of this disclosure. However, this disclosure is not limited to be applied to the configuration of the image forming apparatus 1 but can be applied to any image forming apparatus having different methods. For example, this disclosure is also applicable to an image forming apparatus that employs an inkjet method or to an offset printing machine.

In the above description, the spacer is used as an adjuster. However, the adjuster is not limited thereto. For example, the adjuster may adjust the position of the tip of the nip guide portion 22 a by causing a motor to move the guide holding member.

The configurations according to the above-descried embodiments are not limited thereto. This disclosure can achieve the following aspects effectively.

Aspect 1.

In Aspect 1, a sheet feeding device (for example, the sheet feeding device 41) includes a sheet feeder (for example, the bypass sheet feed roller 17), a sheet separator (for example, the bypass sheet separation roller 20), a guide portion (for example, the nip guide portion 22 a), and an adjuster (for example, the spacer 29 and the replacement thin spacer 129). The sheet feeder is configured to feed a sheet (for example, the sheet P and the plurality of sheets P) loaded on a sheet loader (for example, the bypass bottom plate 40 a). The sheet separator is configured to contact the sheet feeder to separate the sheet fed by the sheet feeder. The guide portion is configured to guide the sheet to a contact portion (for example, the bypass separation nip region N) between the sheet feeder and the sheet separator. The adjuster is configured to adjust a position of a downstream end of the guide portion in a sheet conveyance direction.

When the sheet feeder (for example, the bypass sheet feed roller 17) is driven to start conveyance of the sheet loaded on the sheet loader (for example, the bypass bottom plate 40 a), the leading edge of the sheet enters the guide portion (for example, the nip guide portion 22 a) with a certain angle and contacts the guide portion. Consequently, the direction of conveyance of the sheet is changed, and therefore the sheet is guided while sliding on the guide portion. When the sheet is guided while sliding on the guide portion, the upstream part of the sheet from a position where the sheet contacts the guide portion is warped (curved). Then, after having passed the guide portion, the leading end of the sheet contacts the surface of the sheet separator before entering a contact portion.

The angle of entry of the sheet when the leading end of the sheet contacts the surface of the sheet separator (in other words, the angle of the sheet and the tangent line where the leading end of the sheet contacts the surface of the sheet separator) is determined depending on the position of the downstream end of the guide portion in the sheet conveyance direction. Specifically, as the position of the downstream end of the guide portion in the sheet conveyance direction is shifted away from the contact portion, the position at which the leading end of the sheet contacts the surface of the sheet separator is shifted away from the contact portion, thereby increasing the angle of entry of the sheet.

The position of the downstream end of the guide portion in the sheet conveyance direction varies due to manufacturing errors of the device. Therefore, it is likely that the position of the downstream end of the guide in the sheet conveyance direction is shifted away from the target position from the contact portion. In a case in which the position of the downstream end of the guide portion in the sheet conveyance direction is shifted away from the target position from the contact portion and the angle of entry of the sheet increases, it is likely that the sheet feeding failure occurs when conveying a sheet having high rigidity. In a case in which the angle of entry is large, when the leading end of the sheet contacts the sheet separator, the leading end of the sheet presses (pushes) the sheet separator in a direction that the sheet separator separates from the sheet feeder.

In a case in which a sheet having small rigidity such as a plain paper is conveyed, when the sheet presses (pushes) the sheet separator, the leading end of the sheet is warped (curved) due to the reaction force generated by the sheet separator. Therefore, the sheet separator rotates together with the sheet feeder without being separated from the sheet feeder. Accordingly, the leading end of the sheet is conveyed to the contact portion by the sheet separator.

By contrast, in a case in which a sheet having high rigidity such as a thick paper is conveyed, even when the sheet presses (pushes) the sheet separator, the leading end of the sheet is not warped (curved) due to the reaction force generated by the sheet separator and the sheet presses (pushes) the sheet separator. Consequently, the sheet separator separates from the sheet feeder, and therefore does not rotate together with the sheet feeder. Therefore, the leading end of the sheet cannot receive the sheet conveyance force of the sheet separator. As a result, the leading end of the sheet is not conveyed toward the contact portion, which is likely to cause the sheet feeding failure.

Further, it is also likely that manufacturing error causes variation of the position of the downstream end of the guide portion in the sheet conveyance direction, and the downstream end of the guide portion in the sheet conveyance direction enters the contact portion due to the variation. As the downstream end of the guide portion in the sheet conveyance direction comes into the contact portion, when a plurality of sheets enters the contact portion, the frictional force of the sheet and the guide portion is applied as the conveyance resistance to the sheets after the uppermost sheet, specifically, the second sheet and the subsequent sheets after the second uppermost sheet. Since the guide portion has the coefficient of friction to the sheet when compared with the coefficient of friction of the sheet separator, the conveyance resistance caused by the frictional force with the guide portion becomes lower than the static friction between the uppermost sheet and the second (subsequent) sheet. As a result, no slippage occurs between the uppermost sheet and the second sheet. Therefore, the sheets (i.e., the uppermost sheet and the second sheet) are not separated at the contact portion, and may result in occurrence of multiple sheet feeding.

As described above, if the position of the downstream end of the guide portion in the sheet conveyance direction varies due to manufacturing errors of the device or apparatus, it is likely that the multiple sheet feeding or the sheet feeding failure occurs when feeding a sheet having high rigidity.

In order to address this inconvenience, in the sheet feeding device of Aspect 1, the adjuster is configured to adjust the position of the downstream end of the guide portion in the sheet conveyance direction, so that the adjuster adjusts the position of the downstream end of the guide portion in the sheet conveyance direction to a target position. Accordingly, the multiple sheet feeding or the sheet feeding failure is restrained when feeding a sheet with high rigidity.

Aspect 2.

In Aspect 1, a coefficient of friction of the guide portion (for example, the nip guide portion 22 a) to the sheet (for example, the sheet P) is smaller than a coefficient of friction of the sheet separator (for example, the bypass sheet separation roller 20) to the sheet.

According to this configuration, as described in the embodiments above, even if the leading end of the sheet with high rigidity contacts the guide portion at a steep angle, the leading end of the sheet is guided to the contact portion (for example, the bypass separation nip region N) of the sheet separator and the sheet feeder.

Aspect 3.

In Aspect 1 or Aspect 2, the guide portion (for example, the nip guide portion 22 a) is elastically deformable.

According to this configuration, as described in the embodiments above, the downstream end of the guide portion (for example, the nip guide portion 22 a) in the sheet conveyance direction is caused to follow the surface of the sheet separator (for example, the bypass sheet separation roller 20). Accordingly, even if the position of the guide (for example, the guide 22) including the guide portion (for example, the bypass separation nip region N) in the vertical direction varies due to manufacturing errors (in other words, the position of the sheet face of the sheet in the vertical direction located in the contact portion, for example, the bypass separation nip region, varies due to manufacturing errors), the downstream end of the guide portion in the sheet conveyance direction is located near the contact portion.

Aspect 4.

In any one of Aspects 1 to 3, the sheet feeding device (for example, the sheet feeding device 41) further includes a guide (for example, the guide 22) including the guide portion (for example, the nip guide portion 22 a). The guide is longer than the sheet separator (for example, the bypass sheet separation roller 20) in a width direction of the sheet (for example, the sheet P). The width direction of the sheet is a direction perpendicular to the sheet conveyance direction.

According to this configuration, as described in the embodiments above, the sheet is guided by the guide to an area of the sheet outside the width direction of the sheet separator. Accordingly, the sheet is conveyed stably to the contact portion (for example, the bypass separation nip region N) of the sheet separator and the sheet feeder.

Aspect 5.

In any one of Aspects 1 to 4, the sheet separator (for example, the bypass sheet separation roller 20) is a sheet separation roller (for example, the bypass sheet separation roller 20) configured to rotate together with the sheet feeder (for example, the sheet feed roller 17). The sheet separation roller is supported to contact and separate with respect to the sheet feeder and is biased toward the sheet feeder.

According to this configuration, as described in the embodiments above, when the plurality of sheets (for example, the plurality of sheets P) enters the contact portion (for example, the bypass separation nip region N) between the sheet separator (i.e., the sheet separation roller) and the sheet feeder, the sheet separator does not rotate (in other words, the sheet separation roller stops rotating), thereby separating the plurality of sheets one by one to a single sheet (for example, the sheet P).

Aspect 6.

In any one of Aspects 1 to 5, the downstream end of the guide portion (for example, the nip guide portion 22 a) in the sheet conveyance direction is located upstream, in the sheet conveyance direction, from an upstream end (for example, the position X2) of a region where the downstream end of the guide portion in the sheet conveyance direction contacts both the sheet separator (for example, the bypass sheet feed roller 17) and the sheet feeder (for example, the bypass sheet feed roller 17).

According to this configuration, as described above with reference to FIG. 13, the separation performance is prevented from being affected in the contact portion (for example, the bypass separation nip region N) of the sheet separator and the sheet feeder.

Aspect 7.

In any one of Aspects 1 to 6, the sheet feeding device (for example, the sheet feeding device 41) further includes a guide (for example, the guide 22) including the guide portion (for example, the nip guide portion 22 a). An upstream end (for example, the upstream side end portion γ1) of the guide in the sheet conveyance direction is located downstream from a rotatable range (for example, the swing range c) of the sheet loader (for example, the bypass bottom plate 40 a) in the sheet conveyance direction.

According to this configuration, as described above with reference to FIG. 13, the sheet loader is prevented from being hindered to move.

Aspect 8.

In any one of Aspects 1 to 7, the sheet feeding device (for example, the sheet feeding device 41) further includes a guide (for example, the guide 22), a guide holder (for example, the guide holding member 23), and a base (for example, the base 21). The guide includes the guide portion (for example, the nip guide portion 22 a). The guide holder configured to hold the guide. The guide holder is attached to the base. The adjuster (for example, the spacer 29 and the replacement thin spacer 129) is a spacer (for example, the spacer 29 and the replacement thin spacer 129) disposed between the base and the guide holder.

According to this configuration, as described in the embodiments above, the position of the downstream end of the guide portion (for example, the nip guide portion 22 a) in the sheet conveyance direction is adjusted by simply changing the spacer. In addition, very fine adjustment is performed with a simple configuration.

Aspect 9.

In any one of Aspects 1 to 8, the guide portion (for example, the nip guide portion 22 a) is configured to contact the sheet separator (for example, the bypass sheet separation roller 20).

According to this configuration, as described in the embodiments above, even if the position of the guide (for example, the guide 22) in the vertical direction varies due to manufacturing errors, in other words, even if the position of the sheet face in the vertical direction at the contact portion (for example, the bypass separation nip region N) of the sheet separator and the sheet feeder (for example, the bypass sheet feed roller 17) varies due to manufacturing errors, the downstream end of the guide portion in the sheet conveyance direction is located near the contact portion.

Aspect 10.

In Aspect 10, an image forming apparatus (for example, the image forming apparatus 1) includes a sheet loader (for example, the bypass bottom plate 40 a), the sheet feeding device (for example, the sheet feeding device 41), and an image forming device (for example, the image forming device 7). The sheet loader is configured to load a sheet (for example, the sheet P and the plurality of sheets P). The sheet feeding device is configured to separate the sheet loaded on the sheet loader and feed the sheet. The image forming device is configured to form an image on the sheet fed by the sheet feeding device.

According to this configuration, the sheet feeding failure and the multiple sheet feeding are prevent while restraining an increase in size of the image forming apparatus.

The effects described in the embodiments of this disclosure are listed as most preferable effects derived from this disclosure, and therefore are not intended to limit to the embodiments of this disclosure.

The embodiments described above are presented as an example to implement this disclosure. The embodiments described above are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, or changes can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of the invention, and are included in the scope of the invention recited in the claims and its equivalent.

Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 

What is claimed is:
 1. A sheet feeding device comprising: a sheet feeder configured to feed a sheet loaded on a sheet loader; a sheet separator configured to contact the sheet feeder to separate the sheet fed by the sheet feeder; a guide portion configured to guide the sheet to a contact portion between the sheet feeder and the sheet separator; and an adjuster configured to adjust a position of a downstream end of the guide portion in a sheet conveyance direction.
 2. The sheet feeding device according to claim 1, wherein a coefficient of friction of the guide portion to the sheet is smaller than a coefficient of friction of the sheet separator to the sheet.
 3. The sheet feeding device according to claim 1, wherein the guide portion is elastically deformable.
 4. The sheet feeding device according to claim 1, further comprising a guide including the guide portion, wherein the guide is longer than the sheet separator in a width direction of the sheet, the width direction of the sheet being a direction perpendicular to the sheet conveyance direction.
 5. The sheet feeding device according to claim 1, wherein the sheet separator is a sheet separation roller configured to rotate together with the sheet feeder, and wherein the sheet separation roller is supported to contact and separate with respect to the sheet feeder and is biased toward the sheet feeder.
 6. The sheet feeding device according to claim 1, wherein the downstream end of the guide portion in the sheet conveyance direction is located upstream, in the sheet conveyance direction, from an upstream end of a region where the downstream end of the guide portion in the sheet conveyance direction contacts both the sheet separator and the sheet feeder.
 7. The sheet feeding device according to claim 1, further comprising a guide including the guide portion, wherein an upstream end of the guide in the sheet conveyance direction is located downstream from a rotatable range of the sheet loader in the sheet conveyance direction.
 8. The sheet feeding device according to claim 1, further comprising: a guide including the guide portion; a guide holder configured to hold the guide; and a base to which the guide holder is attached, wherein the adjuster is a spacer disposed between the base and the guide holder.
 9. The sheet feeder according to claim 1, wherein the guide portion is configured to contact the sheet separator.
 10. An image forming apparatus comprising: a sheet loader configured to load a sheet; the sheet feeding device according to claim 1, configured to separate the sheet loaded on the sheet loader and feed the sheet; and an image forming device configured to form an image on the sheet fed by the sheet feeding device. 